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Blomqvist, L., Berg, S. & Sandberg, D. (2019). Distortion in laminated veneer products exposed to relative-humidity variations: Experimental studies and finite-element modelling. BioResources, 14(2), 3768-3779
Open this publication in new window or tab >>Distortion in laminated veneer products exposed to relative-humidity variations: Experimental studies and finite-element modelling
2019 (English)In: BioResources, ISSN 1930-2126, E-ISSN 1930-2126, Vol. 14, no 2, p. 3768-3779Article in journal (Refereed) Published
Abstract [en]

A shortcoming of the laminated bending process is that the product may become distorted after moulding. This study focused on the influence of fibre orientation deviation for individual veneers on the distortion of a moulded shell. The distortion of 90 cross-laminated shells of the same geometrical shape, consisting of seven peeled birch veneers, were studied under relative humidity variation. All the veneers were straight-grained in the longitudinal-tangential plane, but to simulate a deviation in fibre orientation, some of the individual veneers were oriented at an angle of 7° relative to the main orientation of the other veneers in the laminate. A finite element model (FEM) was applied to study the possibility of predicting the results of a practical experiment. The study confirms the well-known fact that deviation in fibre orientation influences shape stability. The results also show how the placement of the abnormal veneer influences the degree of distortion. From this basic knowledge, some improvements in the industrial production were suggested. However, the FE model significantly underestimated the results, according to the empirical experiment, and it did not show full coherence. The survey shows the complexity of modelling the behaviour of laminated veneer products under changing climate conditions and that there is a great need to improve the material and process data to achieve accurate simulations. Examples of such parameters that may lead to distortion are density, annual ring orientation in the cross section of the veneer, the orientation of the loose and tight sides of the veneer, and parameters related to the design of the moulding tool.

Place, publisher, year, edition, pages
North Carolina State Univ Dept Wood & Paper Sci, 2019
Keywords
Birch, Cup, FEM, Veneer, Wood, Twist
National Category
Wood Science
Research subject
Wood Science and Engineering
Identifiers
urn:nbn:se:ltu:diva-73340 (URN)10.15376/biores.14.2.3768-3779 (DOI)000466449000091 ()
Note

Validerad;2019;Nivå 2;2019-04-10 (oliekm)

Available from: 2019-03-28 Created: 2019-03-28 Last updated: 2019-06-12Bibliographically approved
Olofsson, L., Broman, O. & Sandberg, D. (2019). Holistic-Subjective Automatic Grading of Sawn Timber: Sensitivity to Systematic Changes. In: International Wood Machining Seminar: . Paper presented at International Wood Machining Seminar.
Open this publication in new window or tab >>Holistic-Subjective Automatic Grading of Sawn Timber: Sensitivity to Systematic Changes
2019 (English)In: International Wood Machining Seminar, 2019Conference paper, Published paper (Other academic)
Abstract [en]

Holistic-subjective automatic grading of sawn timber by a partial least squares (PLS) regression model required training of the model. This study tests the sensitivity towards systematic changes of a specialized PLS model, trained on a selected type of material suitable for a specific paneling product, when used to grade sawn timber systematically different than the material it was trained on. A sawmills automatic scanning system used cameras to measure knot and bark features on 900 planks. Each plank was split into three boards, and each board was shaped into an indoor paneling product and manually graded as desirable or undesirable at a planing mill. The plank grade was decided as the majority of the board-grade outcome. The knot and bark measurements were used to create a large set of feature variables for each plank that was correlated to the plank’s grade by PLS regression. Of the 900 available planks, 434 planks sawn from top logs were used as a class-balanced specialistic training set, with half of the planks resulting in a majority of desirable boards. The regression model trained on the class-balanced specialistic training set was used to grade a test set of 282 planks, containing 64 planks that by manual classification of automatically captured images were determined to be sawn from butt logs and were systematically different from the training material. The PLS model’s grading accuracy of the planks sawn from top logs was 76%, compared to 70% for the plank sawn from butt logs. The grading outcome resulted in a higher proportion of both delivered planks from the sawmill and received desirable planks by the planing mill when grading planks from top logs as compared to planks from butt logs. The results indicated that a specialistic PLS model should not be used for a generalistic use-case.

Keywords
sawmilling, wood, automatic grading, PLS-regression
National Category
Wood Science
Research subject
Wood Science and Engineering
Identifiers
urn:nbn:se:ltu:diva-74170 (URN)
Conference
International Wood Machining Seminar
Available from: 2019-06-04 Created: 2019-06-04 Last updated: 2019-08-15
Olofsson, L., Broman, O., Skog, J., Fredriksson, M. & Sandberg, D. (2019). Multivariate product adapted grading of Scots pine sawn timber for an industrial customer, part 1: Method development. Wood Material Science & Engineering
Open this publication in new window or tab >>Multivariate product adapted grading of Scots pine sawn timber for an industrial customer, part 1: Method development
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2019 (English)In: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280Article in journal (Refereed) Epub ahead of print
Abstract [en]

Rule-based automatic grading (RBAG) of sawn timber is a common type of sorting system used in sawmills, which is intricate to customise for specific customers. This study further develops an automatic grading method to grade sawn timber according to a customer’s resulting product quality. A sawmill’s automatic sorting system used cameras to scan the 308 planks included in the study. Each plank was split at a planing mill into three boards, each planed, milled, and manually graded as desirable or not. The plank grade was correlated by multivariate partial least squares regression to aggregated variables, created from the sorting system’s measurements at the sawmill. Grading models were trained and tested independently using 5-fold cross-validation to evaluate the grading accuracy of the holistic-subjective automatic grading (HSAG), and compared with a resubstitution test. Results showed that using the HSAG method at the sawmill graded on average 74% of planks correctly, while 83% of desirable planks were correctly identified. Results implied that a sawmill sorting station could grade planks according to a customer’s product quality grade with similar accuracy to HSAG conforming with manual grading of standardised sorting classes, even when the customer is processing the planks further.

Place, publisher, year, edition, pages
Taylor & Francis, 2019
Keywords
Sawn timber, visual grading, customer adoption, discriminant analysis
National Category
Wood Science Other Mechanical Engineering
Research subject
Wood Science and Engineering
Identifiers
urn:nbn:se:ltu:diva-73967 (URN)10.1080/17480272.2019.1617779 (DOI)
Funder
Vinnova, 2018-02749
Available from: 2019-05-16 Created: 2019-05-16 Last updated: 2019-06-10
Olofsson, L., Broman, O., Skog, J., Fredriksson, M. & Sandberg, D. (2019). Multivariate Product Adapted Grading of Scots Pine Sawn Timber for an Industrial Customer, Part 2: Robustness to Disturbances. Wood Material Science & Engineering
Open this publication in new window or tab >>Multivariate Product Adapted Grading of Scots Pine Sawn Timber for an Industrial Customer, Part 2: Robustness to Disturbances
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2019 (English)In: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280Article in journal (Refereed) Epub ahead of print
Abstract [en]

Holistic-subjective automatic grading (HSAG) of sawn timber by an industrial customer's product outcome is possible through the use of multivariate partial least squares discriminant analysis (PLS-DA), shown by part one of this two-part study. This second part of the study aimed at testing the robustness to disturbances of such an HSAG system when grading Scots Pine sawn timber partially covered in dust. The set of 308 clean planks from part one of this study, and a set of 310 dusty planks, that by being stored inside a sawmill accumulated a layer of dust, were used. Cameras scanned each plank in a sawmill's automatic sorting system that detected selected feature variables. The planks were then split and processed at a planing mill, and the product grade was correlated to the measured feature variables by partial least squares regression. Prediction models were tested using 5-fold cross-validation in four tests and compared to the reference result of part one of this study. The tests showed that the product adapted HSAG could grade dusty planks with similar or lower grading accuracy compared to grading clean planks. In tests grading dusty planks, the disturbing effect of the dust was difficult to capture through training.

Place, publisher, year, edition, pages
Taylor & Francis, 2019
Keywords
Sawn timber, visual grading, customer adoption, discriminant analysis
National Category
Wood Science Other Mechanical Engineering
Research subject
Wood Science and Engineering
Identifiers
urn:nbn:se:ltu:diva-73854 (URN)10.1080/17480272.2019.1612944 (DOI)000469741800001 ()2-s2.0-85065546163 (Scopus ID)
Funder
Vinnova, 2018-02749
Available from: 2019-05-06 Created: 2019-05-06 Last updated: 2019-06-25
Gaff, M., Babiak, M., Kačík, F., Sandberg, D., Turčan, M., Hanzlíka, P. & Vondrová, V. (2019). Plasticity properties of thermally modified timber in bending: the effect of chemical changes during modification of European oak and Norway spruce.. Composites Part B: Engineering, 165, 613-625
Open this publication in new window or tab >>Plasticity properties of thermally modified timber in bending: the effect of chemical changes during modification of European oak and Norway spruce.
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2019 (English)In: Composites Part B: Engineering, ISSN 1359-8368, E-ISSN 1879-1069, Vol. 165, p. 613-625Article in journal (Refereed) Published
Abstract [en]

The plasticity of thermally modified European oak (Quercus robur L.) and f thermally modified Norway spruce (Picea abies Karst. (L.)) timber was evaluated in bending, and the plastic properties were related to the changes in chemical composition of the wood after modification. The objective was to gain new knowledge about the properties of materials in the plastic region of the force-deformation diagram in bending. A new software was developed (MATESS) and used to identify important characteristics of the material. This software eliminates shortcomings in current standards, such as simplifications in the evaluation of data when sufficiently sensitive measuring equipment is not available. The characteristics studied were: modulus of rupture (MOR), plastic potential (PP) chord modulus (CHM), the moduli of plasticity (EE), and the moduli of plasticity (EMV, EP). Extractives, lignin, cellulose, holocellulose, and hemicelluloses were analysed chemically to reveal the patterns that occur during the loading of the specimens. Thermal modification has different effects on the mechanical properties of oak and spruce, especially on CHM, EMV and EP, due to their different contents and structures of their chemical components. A strong correlation (r > 0.90) between hemicellulose content and MOR and Pp values was found for both species. The coefficients of determination indicated a very low dependence (r2 < 0.1) of MOR, PP, CHM, EE, EMV and EP, on the average density.

Place, publisher, year, edition, pages
Elsevier, 2019
Keywords
Chord modulus; Tangent modulus; Moduli of plasticity; Limit of proportionality; Middle value of plasticity; Modulus of rupture; Chemical analyses
National Category
Wood Science Other Mechanical Engineering
Research subject
Wood Science and Engineering
Identifiers
urn:nbn:se:ltu:diva-72941 (URN)10.1016/j.compositesb.2019.02.019 (DOI)000462803100056 ()2-s2.0-85061626954 (Scopus ID)
Note

Validerad;2019;Nivå 2;2019-02-25 (inah)

Available from: 2019-02-19 Created: 2019-02-19 Last updated: 2019-04-23Bibliographically approved
Couceiro, J., Lindgren, O., Hansson, L., Söderström, O. & Sandberg, D. (2019). Real-time wood moisture-content determination using dual-energy X-ray computed tomography scanning. Wood Material Science & Engineering
Open this publication in new window or tab >>Real-time wood moisture-content determination using dual-energy X-ray computed tomography scanning
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2019 (English)In: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280Article in journal (Refereed) Epub ahead of print
Abstract [en]

The estimation of the pixel-wise distribution of the moisture content (MC) in wood using X-ray computed tomography (CT) requires two scans of the same wood specimen at different MCs, one of which is known. Image-processing algorithms are needed to compensate for the anisotropic distortion that wood undergoes as it dries. An alternative technique based on dual-energy CT (DECT) to determine MC in wood has been suggested by several authors. The purpose of the present study was to evaluate the hypothesis that DECT can be used for the determination of MC in real time. A method based on the use of the quotient between the linear attenuation coefficients (μ) at different acceleration voltages (the so-called quotient method) was used. A statistical model was created to estimate the MC in solid sapwood of Scots pine, Norway spruce and brittle willow. The results show a regression model with R2 > 0.97 that can predict the MC in these species with a RMSE of prediction of 0.07, 0.04 and 0.11 (MC in decimal format) respectively and at MC levels ranging from the green to the totally dry condition. Individual measurements of MC show an uncertainty of up to ±0.4. It is concluded that under the conditions prevailing in this study, and in studies referred to in this paper, it is not possible to measure MC with DECT.

Place, publisher, year, edition, pages
Taylor & Francis, 2019
Keywords
CT-scanning, dual-energy X-ray absorptiometry, wood drying, attenuation coefficient
National Category
Wood Science Other Mechanical Engineering
Research subject
Wood Science and Engineering
Identifiers
urn:nbn:se:ltu:diva-75497 (URN)10.1080/17480272.2019.1650828 (DOI)
Available from: 2019-08-13 Created: 2019-08-13 Last updated: 2019-08-13
Gaff, M., Kačík, F., Sandberg, D., Babiak, M., Turčani, M., Niemz, P. & Hanzlík, P. (2019). The effect of chemical changes during thermal modification of European oak and Norway spruce on elasticity properties. Composite structures, 220, 529-538
Open this publication in new window or tab >>The effect of chemical changes during thermal modification of European oak and Norway spruce on elasticity properties
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2019 (English)In: Composite structures, ISSN 0263-8223, E-ISSN 1879-1085, Vol. 220, p. 529-538Article in journal (Refereed) Published
Abstract [en]

The elasticity in bending of European oak (Quercus robur L.) and Norway spruce (Picea abies (L.) Karst.) timber was evaluated before and after thermal modificationand related to the changes in chemical composition of the wood as a result of the modification. A new software was developed (MATESS) and used to identify characteristic points on the force-deformation diagram. The modulus of elasticity(MOE), stress at the limit of proportionality (LOP) and elastic potential (PE) were used to describe the wood properties. Extractives, lignin, cellulose, holocellulose, and hemicelluloses were analysed to reveal the patterns that occur during the loading of the specimens. Thermal modification lowers the mechanical properties (MOE, LOP and PE) of oak and spruce wood, and the reduction increases with increasing modification temperature. Changes in chemical composition of thermally modified wood show a strong relationship to the reduction in elasticity properties for bot species.

Place, publisher, year, edition, pages
Elsevier, 2019
Keywords
Modulus of elasticity, Limit of proportionality, Elastic potential, Thermally modified wood
National Category
Other Mechanical Engineering
Research subject
Wood Science and Engineering
Identifiers
urn:nbn:se:ltu:diva-73601 (URN)10.1016/j.compstruct.2019.04.034 (DOI)000465495700047 ()2-s2.0-85064095092 (Scopus ID)
Note

Validerad;2019;Nivå 2;2019-04-11 (johcin)

Available from: 2019-04-11 Created: 2019-04-11 Last updated: 2019-06-18Bibliographically approved
Markström, E., Kuzman, M. K., Bystedt, A. & Sandberg, D. (2019). Use of wood products in multi-storey residential buildings: views of Swedish actors and suggested measures for an increased use. Wood Material Science & Engineering
Open this publication in new window or tab >>Use of wood products in multi-storey residential buildings: views of Swedish actors and suggested measures for an increased use
2019 (English)In: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280Article in journal (Refereed) Epub ahead of print
Abstract [en]

Many studies have shown that wooden buildings in general have a lower climate impact than buildings built of conventional materials such as concrete and steel. In Sweden, however, only about 10% of the multi-dwelling buildings are built with timber frames. The goal of this empirical study is to provide a broad picture of the views of Swedish actors regarding the use of wood products in multi-storey residential buildings and suggest measures for an increased use. A questionnaire concerning the use of wood products in construction was sent out to Swedish developers, main contractors, and architects and 100 answers were received. The study shows that the views of the groups of actors differ in some respects and factors that may either facilitate or be obstacles to an increased use of wood products were identified and discussed.

Keywords
Multi-storey buildings, wood products, Sweden, developers, main contractors, architects
National Category
Other Mechanical Engineering
Research subject
Wood Science and Engineering
Identifiers
urn:nbn:se:ltu:diva-73498 (URN)10.1080/17480272.2019.1600164 (DOI)
Available from: 2019-04-08 Created: 2019-04-08 Last updated: 2019-04-08
Sandberg, D. (2018). Architects' perception of EWPs and modified wood in contemporary timber architecture. In: : . Paper presented at 2018 World Conference on Timber Engineering, WCTE 2018; COEX Convention and Exhibition CenterSeoul; South Korea; 20-23 August 2018.
Open this publication in new window or tab >>Architects' perception of EWPs and modified wood in contemporary timber architecture
2018 (English)Conference paper (Refereed)
Identifiers
urn:nbn:se:ltu:diva-72855 (URN)2-s2.0-85058164622 (Scopus ID)
Conference
2018 World Conference on Timber Engineering, WCTE 2018; COEX Convention and Exhibition CenterSeoul; South Korea; 20-23 August 2018
Available from: 2019-02-12 Created: 2019-02-12 Last updated: 2019-02-12
Couceiro, J., Hansson, L., Ahec, A. & Sandberg, D. (2018). CT-scanning of the drying process of Eucalyptus nitens.. In: Cárcel JA, Polo GC, García-Pérez JV, Mulet A, Rosselló C., (Ed.), Proceedings of 21st International Drying Symposium.: . Paper presented at 21st International Drying Symposium, Valencia, Spain, Sep 11-14, 2018 (pp. 1269-1276). Valencia: Editorial Universitat Politècnica de València
Open this publication in new window or tab >>CT-scanning of the drying process of Eucalyptus nitens.
2018 (English)In: Proceedings of 21st International Drying Symposium. / [ed] Cárcel JA, Polo GC, García-Pérez JV, Mulet A, Rosselló C.,, Valencia: Editorial Universitat Politècnica de València , 2018, p. 1269-1276Conference paper, Published paper (Refereed)
Abstract [en]

The drying of Eucalyptus nitens is a troublesome process as the species is extremely prone to drying defects. This paper reports ongoing research toimprove the understanding of surface checking and cell collapse in Chilean grown Eucalyptus nitens during drying. Computed tomography (CT) scanning was used as a powerful tool for studying the internal changes in the wood-material during the drying process. Different levels of temperatures have been tested with the same equilibrium moisture content (EMC) conditions and low air velocity. The results confirm that a low drying temperature and a low air velocity, which results in a slow rate of drying, reduce internal cell collapse and surface checking .

Place, publisher, year, edition, pages
Valencia: Editorial Universitat Politècnica de València, 2018
Keywords
Cell collapse; computed tomography; surface checks; wood drying; internal checks
National Category
Other Mechanical Engineering
Research subject
Wood Science and Engineering
Identifiers
urn:nbn:se:ltu:diva-71201 (URN)10.4995/ids2018.2018.7380 (DOI)978-84-9048-688-7 (ISBN)
Conference
21st International Drying Symposium, Valencia, Spain, Sep 11-14, 2018
Available from: 2018-10-13 Created: 2018-10-13 Last updated: 2019-05-07Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-4526-9391

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